Vapor generator



3, 1969 w. T. LAWR'ENCE 3,

VAPOR GENERATOR Original Filed Aug. 30, 1967 9 W :1 m z 0' 6 0 010: aux/raw Mad.

United States Patent Office 3,485,216 Patented Dec. 23, 1969 US. Cl. 122-33 4 Claims ABSTRACT OF THE DISCLOSURE Apparatus comprising a casing having a top and bottom with openings therein, heating ducts interconnecting said openings, a boiler comprising a tube which progresses downwardly in the casing with a space between the tube and said ducts, and heat-storage material substantially filling the space to serve as a butler between ducts and tube and to supply heat to the boiler when the heat demand for the boiler is greater than the heater is supplying at any time, and means for circulating combustion gases downwardly through one of said ducts and thence upwardly through another duct, the boiler-tube having a liquid inlet at the top and vapor outlet at the bottom.

This application s a continuation of 664,413, filed Aug. 30, 1967, and now abandoned.

This invention relates to power plants which are particularly adatped to propulsion of vehicles and which utilize heat-storage materials such as sodium hydroxide or other alkali-metal hydroxides. When freshly charged with heat such material may have a temperature of 900 F. or higher and during the operating cycle its temperature at certain points in the system may drop to 300 F. or lower. Withdrawal of heat for vehicle propulsion may be subsequent to or concurrent with charging.

Heat engines of the turbine type or reciprocating engines such as the Stirling or the conventional steam engine may be used as heat-to-power conversion devices. The turbine has the advantage of low weight; the Stirling engine, high efficiency; and a reciprocating engine, the ability to start under load.

For efficient operation such engines must be supplied with high pressure super-heated vapor whose state is controlled within reasonably close limits. The state of the vapor is determined by any two of its properties, the temperature and pressure being most conveniently used in the present invention. The state of steam may, for example, be fixed within a range suitable for a reciprocating engine by maintaining its temperature in the range of 500 to 700 F. and its pressure at approximately 500 psi. Higher temperatures are undesirable because of deleterious eflects on lubricants and metals. The turbine can utilize steam at temperatures of 950 F. and higher, at similar or higher pressures.

In the conventional fuel-fired steam generating system the tubular generating elements have fluid, water or moving steam in direct contact with one side, e.g. the insidesurfaces of the tubes, and the high-temperature combus tion products of the fuel in contact with the other side. The temperature of the combustion products is high enough to damage the tubes unless the water is present or the steam is moving past the surface fast enough to provide the necessary cooling. When the steam or other vapor is used to drive an engine whose speed and power output must be independently variable over wide ranges, a widely varying demand on the generator for vapor results. To obtain reasonable efficiency from the engine, the generator must maintain the desired state of the vapor in spite of the varying demand.

These limitations and requirements lead to complicated and costly systems of controls. An extensive patent literature exists on such control systems. Typical examples are 1,283,109; 1,724,996; 1,732,796 and 3,111,936.

These .show the need in the conventional steam boiler for controlling steam pressure, steam temperature, boiler water level, water injection rate, burner fuel rate, and burner air rate, in order to satisfy the varying demand by the engine with steam of controlled state.

Objects of the present invention are to produce a power plant which is simple and economical in construction, which produces vapor at predetermined pressure and temperature with a minimum of controls, which op crates an engine eflicient throughout wide temperature variations of the source of heat, which is capable of delivering vapor at maximum rate instantly on demand, which permits the heater to operate at maximum efiiciency at all times, which minimizes air pollution in the exhaust, which permits the heat source to be operated at a rate correspondng approximately to the average rather than the maximum demand, which requires a relatively small heater, which allows the burner to operate even with dry boiler tubes without damage to the tubes and which is durable, economical, and reliable in use.

, According to this invention the apparatus comprises a boiler having an inlet and an outlet for connection to a source of liquid supply and the engine respectively, a

casing surrounding the boiler, a heater disposed in the casing. with a space between the boiler and heater, heatstorage material substantially filling said space to serve as a bufferbetween boiler and heater and to supply heat to the boiler when the heat demand for the boiler is greater than the heater is supplying at anytime, and means responsive to. the temperature of the material for controlling the heater, the inlet being inthe upper.-. part of said casing and the outlet being in the lower. part of thecasing and the heater being arranged to heat' the material progressively from top to bottom. Preferably the casing has top and bottom walls with openings therein and the'heater includes a first duct interconnecting said openingsand means for circulating combustion gases or other heating material downwardly through said duct. Inthe preferred embodiment the apparatus has one or more additional ducts'extending between .said top andbottom walls, a manifold interconnecting said additional ducts at the bottom and anexhaust for said additional ducts at the top, said additional ducts are distributed around said first duct an said. temperature-responsive means is located at the top of said space. Alternatively, .the heat may be produced byelectric energy, said ducts being replaced by suitable protective tubes within which resistance heating elements are located.

For thepurpose of illustration a typical embodiment of the invention is shown in the accompanying drawings in which- FIG. 1 is a diagrammatic vertical central section;

FIG. 2 is a section on line 2-2 of FIG. 1; and 6 FIG. 3 is a side view of the boiler coil.

comprises a casing 1 having a boiler chamber defined by a top 2 and a bottom 3 and a combustion chamber 4, all of which may be surrounded by thermal insulation (not shown). Extending through the boiler chamber from a. manifold 5 to an exhaust manifold 6 are gas ducts 7, and a central duct 70 extending from the combustion chamber to the manifold 5. Thus the combustion gases flow downwardly through the central duct 7c and upwardly through the lateral ducts 7. Extending from an inlet 8 to an outlet 9 is a boiler coil 11 leading to an engine or other vapor-operated device, the coil being spaced from the ducts 7. While the coil may have any desired shape it preferably progresses continuously in a downward direction as shown in FIG. 3. The space between coil and fines is filled with sodium hydroxide or other heat-storage material 13. A small clearance space 24 is provided between the surface 23 of the molten sodium hydroxide when at its maximum temperature, and the top 2. Leading to the inlet 8 is a liquid supply duct 14 containing a pump 16. Extending around the pump is by-pass 17 containing a valve 18 responsive to the pressure between inlet 8 and pump 16 to by-pass liquid around the pump when the pressure reaches a predetermined maximum. A fuel burner 19 is controlled by a valve 21 responsive to a thermostat 22 buried in the heat-storage material 13 near the top 2 for closing fuel valve 21 when the temperature of the heat-storage material reaches a predetermined maximum of 650 F. and opening it when the temperature of the material reaches a predetermined minimum of 625 R, which is above the melting point of the material (605 F.). l

The pump 16 delivers liquid at a substantially constant rate which is somewhat in excess of the maximum required by the boiler, the excess circulating through the by-pass 17. The characteristics of the by-pass valve 18 are such that the pressure drop across it changes only slightly as the flow rate through it varies from maximum to minimum, and it maintains a substantially constant pressure in the liquid delivered to the inlet 8 to the boiler. Thus, the desired pressure at 8, e.g. 600 p.s.i., can be maintained within sufiiciently narrow limits regardless of whether the engine is demanding vapor at maximum rate when delivering maximum power, or whether it is demanding almost no vapor when delivering little or no power. The coil 11 is designed with a length and cross-section such that the pressure drop between entrance 8 and exit 9 at maximum through-put is small; consequently the aforesaid control of pressure at entrance 8 provides adequate control over the pressure of the vapor delivered at exit 9. Since the coil is completely surrounded by the heat-storing material which is limited to a maximum temperature of 650 F., the coil cannot be overheated even if no water enters. The coil 11 is designed with enough surface to permit evaporation of all the liquid in its upper section, the vapor being superheated in the lower part.

Sodium hydroxide and other substances preferred as heat-storage materials have thermal expansion coefiieients greater than those of steel and other metals suitable for construction of casing, top, bottom, and flues. Consequently, when the material is being heated through its melting point and above, a channel must be provided to allow the expanding liquid to escape into the clearance space 24; otherwise pressures high enough to damage parts of the system could develop. The configuration described accomplishes this since the gases from the burner in passing downwardly through duct 70 initiate melting at the surface 23 of the heat-storage materials, the melting zone moving progressively down the outer surface of the duct.

The advantages of the system are best realized when the heating rate of the'burner is set to provide slightly more than the average power requirement of the vehicle. When the power requirement is greater, heat is drawn from the heat-storage material, and vice versa. Thus two significant modes of operation occur; one when the heating rate is less than that required by the boiler, and the other when the heating rate is greater than the requirement.

In the former case, assuming that the NaOH starts at a temperature of 650 F. throughout, heat will be withdrawn most rapidly by the uppermost sections of the coil 11, where boiling occurs, cooling the NaOH near thermostate 22 to the lower control. temperature of 625 F. However, thermal convection and agitation by the motion of the vehicle will cause circulation of the liquid producingiand maintaining a uniform temperature from top to bottom. When the freezing temperature is reached, solidification progresses downwardly from the top, with the liquid below remaining at the melting point. In the production of steam at 600 F. and 600 p.s.i., suitable for operating eificiently a reciprocating engine, approximately 87% of the heat required is used to evaporate the liquid, at 486 F. and only 13% to superheat it to 600 F. Thus in the lower part of the coil 11, the circulating liquid NaOH at its melting point of 605 F. insures that the desired temperature of the steam will be maintained as long as an appreciable amount of liquid NaOH persists in the system. In cooling from 650 F. to its melting point and solidifying, each pound of NaOH releases approximately B.t.u. of heat. To maintain the vapor within a predetermined temperature range, of course the heatstorage material in the region of the vapor outlet must operate in a somewhat higher range because of the temperature gradient between the material and the vapor. The system is designed with sufiicient heat transfer surface between the coil and the heat-storage material to insure that the superheated steam issuing from the coil is close to the temperature of the material at its melting point.

Other temperatures in the superheated vapor can be produced by the use of other heat-storage materials; for example, lithium hydroxide having a melting point of 880 F. with a latent heat of fusion of 375 B.t.u./lb. is a preferred material for producing steam having a temperature of 880 F. Intermediate temperatures can be obtained through the use of mixtures of alkali metal hydroxides with the eutectic mixtures being especially useful.

It should be understood that the present disclosure is for the purpose of illustration only and that this invention includes all modifications and equivalents which fall within the scope of the appended claims.

I claim:

1. For supplying heated fluid at a predetermined state within a predetermined temperature range, apparatus comprising a fluid heating tube having an inlet for connection to a source of liquid supply and an outlet, a casing surrounding the tube, a heater disposed in the casing with a space between the tube and heater, heat-storage material substantially fillingsaid space to serve as a buffer between tube and heater and to supply heat to the tube when the heat demand is greater than the heater is supplying at any time, and means responsive to the temperature of the material for controlling 'the heater, characterized in that the melting point of said material is within said range so that the latent heat of fusion helps to keep the temperature of the fluid from falling below said range and in that said inlet is in the upper part of said casing and the outlet is in the lower part of the casing and in that said temperature-responsive means is located at the top of the casing.

2. Apparatus according to claim 1 wherein said casing has top and bottom walls with openings therein and said heater includes a duct interconnecting said openings and means for circultating combustion gases or other heating material downwardly through said duct.

3. Apparatus according to claim 2 further characterized by one or more additional ducts extending between said top and bottom walls, a manifold interconnecting 5 6 said ducts at the bottom and an exhaust for said additional 2,383,924 8/ 1945 Way et a1. 122-182 ducts at the top. 3,062,510 11/1962 'Percival 12232 XR 4. Apparatus according to claim 3 wherein said addi- 3,127,936 4/1964 Eurenius 126 -400 XR tional ducts are distributed around said first duct. 3,314,400 4/1967 Sarrat et a1 12233 3,196.841 7/1965 Loebel 12233 References Cited 5 I UNITED STATES PATENTS KENNETH W. SPRAGUE, Primary Examlner 2,911,513 11/1959 MaeCracken 126-400 US. Cl. X.R.

2,791,204 5/1957 Andrus 12233 126-400 

